Smoke retardant vinyl chloride and vinylidene chloride polymer compositions

ABSTRACT

Smoke retardant vinyl chloride and vinylidene chloride polymer compositions are obtained by including therein a synergistic mixture of (A) at least one nickel compound selected from the group consisting of NiCl 2 , NiCO 3  NiMoO 4 , NiO, Ni 2  O 3 , NiS, NiSO 4 , NiWO 4 , nickel citrate and nickel formate, and (B) at least one bismuth compound selected from the group consisting of BiBO 3 , Bi 2  O 3 , Bi 2  O 2  CO 3 , and Bi 2  S 3 . Substantial smoke retardation is also obtained by including the above nickel compounds or bismuth compounds individually or the following nickel compounds or bismuth compounds individually in the vinyl chloride or vinylidene chlorides polymer compositions: NiB 2 , NiCrO 4 , NiFe 2  O 4 , NiI 2 , Ni 3  (PO 4 ) 2 , Ni 2  Si, NiSnO 3 , nickel acetylacetonate, BiI 3 , or BiPO 4 .3H 2  O.

BACKGROUND OF THE INVENTION

Vinyl chloride and vinylidene chloride polymers are known to be self-extinguishing and relatively more flame retardant than other polymers such as polyethylene, polypropylene and the like. However, a substantial amount of smoke may be produced upon exposure of vinyl chloride and vinylidene chloride polymers to a flame. Conventional flame retardants such as antimony oxide do not aid in smoke reduction.

The following prior art is related to the present invention. Nickel oxides or bismuth oxides are effective in amounts up to several percent as condensing agents for polyvinyl halides. (U.S. Pat. No. 2,157,997). Bismuth oxide is a known vinyl chloride polymer flame retardant, either alone or mixed with certain other materials; see U.S. Pat. No. 2,590,211, U.S. Pat. Off. Def. Publ. 892,010 (76 Chem. Abs. 73666a), 2 Brit. Polym.J. 249-253(1970) (73 Chem. Abs.131605f), and Germ. 1,201,544 (63 Chem. Abs. 15.61e). Bi₂ S₃ is a known vinyl chloride polymer flame retardant (U.S. Pat. No. 2,590,211). The fact that an additive is a flame retardant does not mean that it will have good smoke retardant properties, as is well known to those skilled in the art. New smoke retardant vinyl chloride and vinylidene chloride polymer compositions are desired.

SUMMARY OF THE INVENTION

Smoke retardant vinyl chloride and vinylidene chloride polymer compositions are obtained by including therein a synergistic mixture of (A) at least one nickel compound selected from the group consisting of NiCl₂, NiCO₃, NiMoO₄, NiO, Ni₂ O₃, NiS, NiSO₄, NiWO₄, nickel citrate and nickel formate and (B) at least one bismuth compound selected from the group consisting of BiBO₃, Bi₂ O₃, Bi₂ O₂ CO₃ and Bi₂ S₃. Substantial smoke retardation is also obtained by including these nickel compounds or bismuth compounds individually in the vinyl chloride or vinylidene chloride polymer compositions: NiB₂, NiCl₂, NiCO₃, NiCrO₄, NiFe₂ O₄, NiI₂, NiMoO₄, Ni₃ (PO₄)₂, NiS, NiSnO₃, NiSO₄, NiWO₄, nickel citrate, nickel formate, nickel acetylacetonate, BiBO₃, BiI₃, Bi₂ O₂ CO₃ or BiPO₄.3H₂ O.

DETAILED DESCRIPTION

The following compounds are novel additives in vinyl chloride and vinylidine chloride polymer compositions and are effective individually as smoke retardants: NiB₂, NiCl₂, NiCO₃, NiCrO₄, NiFe₂ O₄, NiI₂, NiMoO₄, Ni₃ (PO₄)₂, NiS, NiSnO₃, NiSO₄, NiWO₄, nickel citrate, nickel formate, nickel acetylacetonate, BiBO₃, BiI₃, Bi₂ O₂ CO₃ or BiPO₄.3H₂ O. Moreover, the present invention also encompasses vinyl chloride and vinylidene chloride polymer compositions containing therein synergistic mixtures of (A) at least one nickel compound selected from the group consisting of NiCl₂, NiCO₃, NiMoO₄, NiO, Ni₂ O₃, NiS, NiSO₄, NiWO₄, nickel citrate and nickel formate, and (B) at least one bismuth compound selected from the group consisting of BiBO₃, Bi₂ O₃, Bi₂ O₂ CO₃, and Bi₂ S₃.

Vinyl chloride and vinylidene chloride polymers used in this invention include homopolymers, compolymers and blends of homopolymers and/or copolymers. The vinyl chloride and vinylidene chloride polymers may contain from 0 up to about 50% by weight of at least one other vinylidene monomer (i.e., a monomer containing at least one terminal CH₂ =C< group per molecule) copolymerized therewith, more preferably up to about 20% by weight of such monomer. These monomers include 1-olefins having from 2 to 12 carbon atoms, more preferably from 2 to 8 carbon atoms, such as ethylene, propylene, 1-butene, isobutylene, 1-hexane, 4-methyl-1-pentene and the like; dienes having from 4 to 10 carbon atoms including conjugated dienes as butadiene, isoprene, piperylene and the like; ethylidene norbornene and dicyclopentadiene; vinyl esters and allyl esters such as vinyl acetate, vinyl chloroacetate, vinyl propionate, vinyl laurate, allyl acetate and the like; vinyl aromatics such as styrene, α-methyl styrene, chlorostyrene, vinyl toluene, vinyl naphthalene and the like; vinyl and allyl ethers and ketones such as vinyl methyl ether, allyl methyl ether, vinyl isobutyl ether, vinyl n-butyl ether, vinyl chloroethyl ether, methyl vinyl ketone and the like; vinyl nitriles such as acrylonitrile, methacrylonitrile and the like; cyanoalkyl acrylates such as α-cyanomethyl acrylate, the α-, β- and γ-cyanopropyl acrylates and the like; olefinically unsaturated carboxylic acid and esters thereof, including α,β-olefinically unsaturated acids and esters thereof such as methyl acrylate, ethyl acrylate, chloropropyl acrylate, butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate, cyclohexyl acrylate, phenyl acrylate, glycidyl acrylate, methoxyethyl acrylate, ethoxyethyl acrylate, hexythioethyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, glycidyl methacrylate and the like, and including esters of maleic and fumaric acid and the like; amides of the α,β-olefinically unsaturated carboxylic acids such as acrylamide and the like; divinyls, diacrylates and other polyfunctional monomers such as divinyl benzene, divinyl ether, diethylene glycol diacrylate, ethylene glycol dimethacrylate, methylenebis-acrylamide, allyl pentaerythritol, and the like; bis(β-haloalkyl) alkenyl phosphonates such as bis(β-chloroethyl) vinyl phosphonate and the like; and the like.

More preferred monomers include 1-olefins having from 2 to 12 carbon atoms, more preferably from 2 to 8 carbon atoms, such as ethylene, propylene, 1-butene, isobutylene, 1-hexene, 4-methyl-1-pentene and the like; vinyl esters and allyl esters such as vinyl acetate, vinyl chloroacetate, vinyl propionate, vinyl laurate, allyl acetate and the like; olefinically unsaturated carboxylic acids and esters thereof, including α,β-olefinically unsaturated acids and esters thereof such as methyl acrylate, ethyl acrylate, chloropropyl acrylate, butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate, cyclohexyl acrylate, phenyl acrylate, glycidyl acrylate, methoxyethyl acrylate, ethoxyethyl acrylate, hexylthioacrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, glycidyl methacrylate and the like, and including esters of maleic and fumaric acid and the like; and amides of α,β-olefinically unsaturated carboxylic acids such as acrylamide and the like.

More preferred smoke retardant synergistic mixtures include (A) at least one nickel compound selected from the group consisting of NiO and Ni₂ O₃ and (B) at least one bismuth compound selected from the group consisting of Bi₂ O₃ and Bi₂ O₂ CO₃. More preferred individual smoke retardant additives include NiCO₃, NiBO₃, and Bi₂ O₂ CO₃. Supporting media such as Al₂ O₃, SiO₂ and other substantially inert inorganic supporting materials known in the art may be used for the smoke retardant additives and in many cases are preferred, since additive surface area is greatly increased for smoke reduction purposes.

Not all nickel compound/bismuth compound mixtures are synergistic, and it is difficult or impossible to predict synergism. Mixtures found to be nonsynergistic include NiB₂ and BiPO₄.3H₂ O, nickel stearate and bismuth salicylate, nickel acetylacetonate and BiI₃, and Ni₃ (PO₄)₂ and Bi₂ O₂ CO₃. Other nonsynergistic combinations include nickel metal and bismuth metal, nickel borate and Bi₂ O₂ CO₃, NiCl₂ and bismuth metal, and NiO and bismuth metal. Thus, it was surprising and unexpected to find synergistic smoke reduction using the specific nickel compound/bismuth compound mixtures of this invention.

The additive compounds used in this invention are polycrystalline or amorphous fine powders, preferably with an average particle size less than about 200 microns, more preferably from about 0.5 to about 150 microns. Polymer compositions containing the additives of this invention may have colors similar to, although somewhat lighter than, the additives themselves. The additive compounds are used in total amounts from about 0.25 to about 20 parts by weight per 100 parts by weight of polymer. Use of more than about 20 parts by weight of additive per 100 parts by weight of polymer probably will affect adversely other important physical properties, such as tensile strength and the like.

The vinyl chloride and vinylidene chloride polymers may be prepared by any method known to the art such as by emulsion, suspension, bulk or solution polymerization. The additive compounds may be mixed with the polymer emulsion, suspension, solution or bulk mass before monomer recovery and/or drying. More preferably the compounds may be mixed with dry granular or powdered vinyl halide polymers. The polymer and compound may be mixed thoroughly in granular or powder form in apparatus such as a Henschel mixer and the like. Alternatively, this step may be eliminated and the mixing done while the polymer mass is fluxed, fused and masticated to homogeneity under fairly intensive shear in or on a mixer apparatus having its metal surface in contact with the material. The fusion temperature and time will vary according to the polymer composition and level of additive compound but will generally be in the range of about 300° to 400°F and 2 to 10 minutes.

Smoke retardancy may be measured using an NBS Smoke Chamber according to procedures described by Gross et al, "Method for Measuring Smoke from Burning Materials," Symposium on Fire Test Methods -- Restraint & Smoke 1966, ASTM STP 422, pp. 166-204. Maximum smoke density (D_(m)) is a dimensionless number and has the advantage of representing a smoke density independent of chamber volume, specimen size or photometer path length, provided a consistent dimensional system is used. Maximum rate of smoke generation (R_(m)) is defined in units of min⁻ ¹. Percent smoke reduction is calculated using this equation: ##EQU1## The term "D_(m) /gram" means maximum smoke density per gram of sample. D_(m) and other aspects of the physical optics of light transmission through smoke are discussed fully in the above ASTM publication.

Smoke retardancy may be measured quickly using the Goodrich Smoke-Char Test. Test samples may be prepared by dry blending polymer resin and smoke retardant additives. The blend is ground in a liquid N₂ -cooled grinder to assure uniform dispersion of the smoke retardant additives in the resin. Small (about 0.3 g) samples of the polymer blend are pressed into pellets about 1/4 inch in diameter for testing. Alternatively, test samples may be prepared by blending resin, smoke retardant additives and lubricant(s) or processing aid(s) in a blender such as an Osterizer blender. The blend is milled, pressed into sheets, and cut into small (about 0.3 gram) samples for testing. The test samples are placed on a screen and burned for 60 seconds with a propane gas flame rising vertically from beneath the sample. Sample geometry at a constant weight has been found not to be significant for the small samples used in this test. A Bernz-O-Matic pencil flame burner head is used with gas pressure maintained at 40 psig. The sample is immersed totally and continuously in the flame. Smoke from the burning sample rises in a vertical chimney and passes through the light beam of a Model 407 Precision Wideband Photometer (Grace Electronics, Inc., Cleveland, Ohio) coupled with a photometer integrator. Smoke generation is measured as integrated area per gram of sample.

The vinyl chloride and vinylidene chloride polymer compositions of this invention may contain the usual compounding ingredients known to the art such as fillers, stabilizers, opacifiers, lubricants, processing aids, impact modifying resins, plasticizers, antioxidants and the like.

The following examples illustrate the present invention more fully.

EXAMPLES 1 - 6

The following recipe was used:

    MATERIAL                PARTS                                                  ______________________________________                                         Polyvinyl Chloride*     100.0                                                  Polyethylene Powder Processing Aid                                                                      1.5                                                   Additive (A)**          Variable                                               Additive (B)***         Variable                                               ______________________________________                                          *Homopolymer having an inherent viscosity of about 0.92-0.99; ASTM             classification GP-4-15443.                                                     **Nickel compound selected from the group consisting of NiCl.sub.2,            NiCO.sub.3, NiMoO.sub.4, NiO, Ni.sub.2 O.sub.3, NiS, NiSO.sub.4,               NiWO.sub.4, nickel citrate and nickel formate. The control sample              contained no additive.                                                         ***Bismuth compound selected from the group consisting of BiBO.sub.3,          Bi.sub.2 O.sub.3, Bi.sub.2 O.sub.2 CO.sub.3, and Bi.sub.2 S.sub.3. The         control sample contained no additive.                                    

Each experimental sample was prepared by milling the recipe material on a two-roll mill for about 5 minutes at a roll surface temperature of about 320°F. The milled samples were pressed into 6 in. × 6 in. × 0.050 in. sheets, except for examples 2 and 4, which were pressed into 6 in. × 6 in. × 0.075 in. sheets. Pressing was done at about 310° - 320°F. using 40,000 lbs. of force applied to a 4-inch ram. The samples were given a 2-minute preheat prior to pressing for 8 minutes under full load.

The molded samples were cut into 3 in. × 3 in. × 0.050 in. sections, except for examples 2 and 4, which were cut into 3 in. × 3 in. × 0.075 in. sheets. The sections were tested using the flaming mode of the NBS Smoke Chamber Test (ASTM STP 422, pp. 166-204) described heretofore. Test results are given in Table I.

                                      TABLE I                                      __________________________________________________________________________                            Maximum                                                                        Rate of Smoke                                                                           Maximum Smoke                                       Additive (A)                                                                            Additive (B)                                                                            Generation                                                                              Density per Gram of                            Example                                                                             (phr)    (phr)    (R.sub.m, min.sup.-.sup.1)                                                              Sample (D.sub.m /g)                                                                        Smoke Reduction                    __________________________________________________________________________                                                 (%)                                Control                                                                             (No Additive)                                                                           (No Additive)                                                                           556      68.6        --                                 1    NiO (10)          111      32.9        52.0                                    --       Bi.sub.2 O.sub.3 (10)                                                                   209      25.4        63.0                                    NiO (5)  Bi.sub.2 O.sub.3 (5)                                                                     78      16.4        76.0                                2*  NiO (10) --       --       33.6        51.0                                    --       Bi.sub.2 O.sub.2 CO.sub.3 (10)                                                          --       25.5        62.0                                    NiO (5)  Bi.sub.2 O.sub.2 CO.sub.3 (5)                                                           --       11.9        82.6                                    NiO (7)  Bi.sub.2 O.sub.2 CO.sub.3 (3)                                                           --       10.8        84.3                                    NiO (3)  Bi.sub.2 O.sub.2 CO.sub.3 (7)                                                           --       19.1        72.2                               3    NiO (10) --       111      32.9        52.0                                    --       BiBO.sub.3 (10)                                                                          95      21.0        69.4                                    NiO (5)  BiBO.sub.3 (5)                                                                           98      15.4        77.6                                4*  Ni.sub.2 O.sub.3 (10)                                                                   --       315      34.5        49.7                                    --       Bi.sub.2 O.sub.2 CO.sub.3 (10)                                                          --       24.5        62.8                                    Ni.sub.2 O.sub.3 (5)                                                                    Bi.sub.2 O.sub.2 CO.sub.3 (5)                                                           --       21.5        68.7                               5    NiS (10) --       280      58.2        15.0                                    --       Bi.sub.2 O.sub.2 CO.sub.3 (10)                                                          109      24.5        64.3                                    NiS (5)  Bi.sub.2 O.sub.2 CO.sub.3 (5)                                                           128      20.1        70.7                               6    NiWO.sub.4 (6)                                                                          --       263      41.8        39.1                                    --       Bi.sub.2 O.sub.2 CO.sub.3 (6)                                                           --       20.2        70.5                                    NiWO.sub.4 (4)                                                                          Bi.sub.2 O.sub.2 CO.sub.3 (2)                                                           115      19.3        71.9                               __________________________________________________________________________      *Sample size was 3 in. × 3 in. × 3 in. × 0.075 in.     

The above results demonstrate that the additive mixtures used in this invention are synergistic and substantially retard smoke formation during burning of rigid polyvinyl chloride in the NBS Smoke Chamber (ASTM STP 422, pp. 166-204). The results also demonstrate the smoke retardant effects of individual additives in the same test.

EXAMPLES 7 - 13

The following recipe was used:MATERIAL PARTS______________________________________Polyvinyl Chloride* 100.0Additive (A)** VariableAdditive (B)*** Variable______________________________________ *Homopolymer having an inherent viscosity of about 0.92 - 0.99; ASTM classification GP-4-15443. **Nickel compound selected from the group consisting of NiCl₂, NiCO₃, NiMoO₄, NiO, Ni₂ O₃, NiS, NiSO₄, NiWO₄, nickel citrate and nickel formate. ***Bismuth compound selected from the group consisting of BiBO₃, Bi₂ O₃, Bi₂ O₂ CO₃ and Bi₂ S₃.

Each experimental sample was prepared by blending resin and additives in a liquid N₂ -cooled grinder to assure uniform dispersion of the smoke retardant additives in the resin. Small (about 0.3 gram) samples of the polymer blend were pressed into pellets about 1/4 inch in diameter and tested using the Goodrich Smoke-Char Test described heretofore. Test results are given in Table II. .

                                      TABLE II                                     __________________________________________________________________________          Additive (A)                                                                               Additive (B)                                                                            Smoke Formation per                                  Example                                                                             (phr)       (phr)    Gram of Sample                                                                             Smoke Reduction (%)                      __________________________________________________________________________     Control                                                                             None        None     67.4        --                                       7    NiCl.sub.2 (10)                                                                            --       22.1        67.2                                          --          Bi.sub.2 O.sub.2 CO.sub.3 (10)                                                          12.5        81.5                                          NiCl.sub.2 (5)                                                                             Bi.sub.2 O.sub.2 CO.sub.3 (5)                                                            9.2        86.4                                     8    NiCO.sub.3 (10)                                                                            --       38.7        42.6                                          --          Bi.sub.2 S.sub.3 (10)                                                                   20.8        69.1                                          NiCO.sub.3 (5)                                                                             Bi.sub.2 S.sub.3 (5)                                                                    14.6        78.3                                     9    NiMoO.sub.4 (6)                                                                            --       21.4        68.2                                          --          Bi.sub.2 O.sub.2 CO.sub.3 (6)                                                           27.0        59.9                                          NiMoO.sub.4 (4)                                                                            Bi.sub.2 O.sub.2 CO.sub.3 (2)                                                           17.4        74.2                                     10   NiSO.sub.4 (10)                                                                            --       18.9        72.0                                          --          Bi.sub.2 O.sub.2 CO.sub.3 (10)                                                          12.5        81.5                                          NiSO.sub.4 (5)                                                                             Bi.sub.2 O.sub.2 CO.sub.3 (5)                                                           11.0        83.7                                     11   Nickel Citrate (10)                                                                        --       34.6        48.7                                          --          Bi.sub.2 O.sub. 2 CO.sub.3 (10)                                                         12.5        81.5                                          Nickel Citrate (5)                                                                         Bi.sub.2 O.sub.2 CO.sub.3 (5)                                                           10.9        83.8                                     12   Nickel Formate (10)                                                                        --       36.3        46.1                                          --          Bi.sub.2 O.sub.2 CO.sub.3 (10)                                                          12.5        81.5                                          Nickel Formate (5)                                                                         Bi.sub.2 O.sub.2 CO.sub.3 (5)                                                           11.9        82.3                                     13   NiO (10)    --       24.7        63.4                                          --          Bi.sub.2 O.sub.3 (10)                                                                   20.7        69.3                                          NiO (5)     Bi.sub.2 O.sub.3 (5)                                                                    10.1        85.0                                     __________________________________________________________________________

The above results demonstrate that the defined additive mixtures substantially reduce smoke evolution during forced burning of rigid polyvinyl chloride in the Goodrich Smoke-Char Test. The results also demonstrate the smoke retardant effects of individual additives in the same test.

EXAMPLES 14 - 23

The following recipe was used:MATERIAL PARTS______________________________________Polyvinyl Chloride* 100.0Polyethylene Powder Processing Aid 1.5Smoke Retardant Additive Variable______________________________________ *Homopolymer having an inherent viscosity of about 0.92 - 0.99; ASTM classification GP-4-15443.

Each experimental sample was prepared using the same experimental preparation procedure and NBS Smoke Chamber Test as for example 1 - 6. Test results are given in Table III.

                                      TABLE III                                    __________________________________________________________________________                          Maximum                                                                        Rate of Smoke                                                                           Maximum Smoke                                                         Generation                                                                              Density per Gram                                 Example                                                                             Additive (phr)  (R.sub.m, min.sup.-.sup.1)                                                              of Sample (D.sub.m /g)                                                                   Smoke Reduction                        __________________________________________________________________________                                             (%)                                    Control                                                                             None            556      68.6      --                                     14   NiB.sub.2 (6)   460      55.2      19.5                                   15   NiI.sub.2 (5)   191      35.9      47.7                                   16   NiFe.sub.2 O.sub.4 (5)                                                                         218      18.8      72.5                                   17   Ni.sub.3 (PO.sub.4).sub.2 (5)                                                                  274      56.8      17.2                                   18   Ni.sub.3 (PO.sub.4).sub.2 (6)                                                                  294      32.0      53.3                                   19   NiSnO.sub.3 (6) 105      22.0      67.9                                   20   Ni.sub.2 Si (10)                                                                               451      53.4      22.1                                   21   Nickel Acetylacetonate (10)                                                                    183      45.8      33.2                                   22   BiI.sub.3 (10)   60      14.7      78.5                                   23   BiPO.sub.4.3H.sub.2 O (6)                                                                      258      25.0      63.5                                   __________________________________________________________________________

The above results demonstrate that the defined additives substantially reduce smoke evolution during forced burning of rigid polyvinyl chloride in the NBS Smoke Chamber (ASTM STP 422, pp. 166 - 204).

EXAMPLES 24 - 32

The following recipe was used:

Each experimental sample was prepared using the same experimental preparation procedure and Goodrich Smoke/Char Test as for examples 7 - 13. Test results are given in Table IV.

                                      TABLE IV                                     __________________________________________________________________________                          Smoke Formation per                                       Example                                                                             Additive (phr)  Gram of Sample                                                                             Smoke Reduction (%)                           __________________________________________________________________________     Control                                                                             None            67.4        --                                            24   NiB.sub.2 (6)   60.4        10.3                                          25   NiCrO.sub.4 (10)                                                                               44.4        34.1                                          26   NiFe.sub.2 O.sub.4 (5)                                                                         25.2        62.6                                          27   Ni.sub.3 (PO.sub.4).sub.2 (6)                                                                  40.5        39.9                                          28   NiSnO.sub.3 (6) 22.7        66.3                                          29   Ni.sub.2 Si (10)                                                                               63.1         6.4                                          30   Nickel Acetylacetonate (10)                                                                    39.6        41.2                                          31   BiI.sub.3 (10)  10.7        84.1                                          32   BiPO.sub.4.3H.sub.2 O (6)                                                                      10.9        83.8                                          __________________________________________________________________________

The above results demonstrate that the defined additives substantially reduce smoke evolution during forced burning of rigid polyvinyl chloride in the Goodrich Smoke/Char Test.

The improved smoke retardant vinyl chloride and vinylidene chloride polymer compositions of this invention are useful wherever smoke resistance is desirable, such as in carpets, house siding, plastic components for airplane interiors, and the like. Of course, overall suitability for a particular use will depend upon other factors as well, such as comonomer type and level, compounding ingredient type and level, polymer particle size, etc. 

I claim:
 1. A smoke retardant composition comprising a vinyl chloride or vinylidene chloride polymer together with (A) at least one nickel compound selected from the group consisting of NiCl₂, NiCO₃, NiMoO₄, NiO, Ni₂ O₃, NiS, NiSO₄, NiWo₄, nickel citrate and nickel formate, and (B) at least one bismuth compound selected from the group consisting of BiBO₃, Bi₂ O₃, Bi₂ O₂ CO₃ and Bi₂ S₃, said compounds (A) and (B) being present in a total amount from about 0.25 to about 20 weight parts per 100 weight parts of polymer.
 2. A composition of claim 1 wherein said polymer contains copolymerized therewith up to about 50% by weight of at least one other vinylidene monomer containing at least one terminal CH₂ =C< group per molecule.
 3. A composition of claim 2 wherein said polymer contains copolymerized therewith up to about 20% by weight of said other vinylidene monomer.
 4. A composition of claim 3 wherein said other vinylidene monomer is selected from the group consisting of 1-olefins containing from 2 to 12 carbon atoms, vinyl esters, α,β-olefinically unsaturated carboxylic acids and esters thereof, amides of α,β-olefinically unsaturated carboxylic acids, and esters of fumaric and maleic acid.
 5. A composition of claim 4 wherein said compound has an average particle size less than about 200 microns.
 6. A composition of claim 5 wherein said compound (A) is NiO and said compound (B) is Bi₂ O₃.
 7. A composition of claim 5 wherein said compound (A) is NiO and said compound (B) is Bi₂ O₂ CO₃.
 8. A composition of claim 5 wherein said compound (A) is NiO and said compound (B) is BiBO₃.
 9. A composition of claim 5 wherein said compound (A) is Ni₂ O₃ and said compound (B) is Bi₂ O₂ CO₃.
 10. A composition of claim 5 wherein said compound (A) is NiS and said compound (B) is Bi₂ O₂ CO₃.
 11. A composition of claim 5 wherein said compound (A) is NiWO₄ and said compound (B) is Bi₂ O₂ CO₃.
 12. A composition of claim 5 wherein said compound (A) is NiCl₂ and said compound (B) is Bi₂ O₂ CO₃.
 13. A composition of claim 5 wherein said compound (A) is NiCO₃ and said compound (B) is Bi₂ S₃.
 14. A composition of claim 5 wherein said compound (A) is NiMoO₄ and said compound (B) is Bi₂ O₂ CO₃.
 15. A composition of claim 5 wherein said compound (A) is NiSO₄ and said compound (B) is Bi₂ O₂ CO₃.
 16. A composition of claim 5 wherein said compound (A) is nickel citrate and said compound (B) is Bi₂ O₂ CO₃.
 17. A composition of claim 5 wherein said compound (A) is nickel formate and said compound (B) is Bi₂ O₂ CO₃.
 18. A smoke retardant composition comprising a vinyl chloride or vinylidene chloride polymer together with a compound selected from the group consisting of NiB₂, NiCO₃, NiCrO₄, NiFe₂ O₄, Ni₃ (PO₄)₂, NiS, NiSnO₃, NiSO₄, NiWO₄, nickel citrate, BiBO₃, Bi₂ O₂ CO₃ and BiPO₄.3H₂ O, said compound being present in an amount from about 0.25 to about 20 weight parts per 100 weight parts of polymer.
 19. A composition of claim 18 wherein said polymer contains copolymerized therewith up to about 50% by weight of at least one other vinylidene monomer containing at least one terminal CH₂ =C< group per molecule.
 20. A composition of claim 19 wherein said polymer contains copolymerized therewith up to about 20% by weight of said other vinylidene monomer.
 21. A composition of claim 20 wherein said other vinylidene monomer is selected from the group consisting of 1-olefins containing from 2 to 12 carbon atoms, vinyl esters, α, β-olefinically unsaturated carboxylic acids and esters thereof, amides of α,β-olefinically unsaturated carboxylic acids, and esters of fumaric and maleic acid.
 22. A composition of claim 21 wherein said compound has an average particle size less than 200 microns.
 23. A composition of claim 22 wherein said compound is NiB₂.
 24. A composition of claim 22 wherein said compound is NiCO₃.
 25. A composition of claim 22 wherein said compound is NiCrO₄.
 26. A composition of claim 22 wherein said compound is NiFe₂ O₄.
 27. A composition of claim 22 wherein said compound is Ni₃ (PO₄)₂.
 28. A composition of claim 22 wherein said compound is NiS.
 29. A composition of claim 22 wherein said compound is NiSnO₃.
 30. A composition of claim 22 wherein said compound is NiSO₄.
 31. A composition of claim 22 wherein said compound is NiWO₄.
 32. A composition of claim 22 wherein said compound is nickel citrate.
 33. A composition of claim 22 wherein said compound is BiBO₃.
 34. A composition of claim 22 wherein said compound is Bi₂ O₂ CO₃.
 35. A composition of claim 22 wherein said compound is BiPO₄.3H₂ O. 